Five frontier LLMs fact-checked the same 1,000 claims. They disagree on 63% of them.

Frontier LLMs often achieve similar results on public benchmarks, which can lead to the belief that they can be used interchangeably to verify facts. We took the 1,000 most recent claims submitted by users to a fact-checking platform and measured the disagreement between five frontier models. We asked each model to assign a verdict to every claim on a five-point scale from True to False and to report its confidence in that verdict. Among the 997 claims for which all five models returned a usable...